I would choose one of the Epcot resorts on Crescent Lake (BWI, BC, or YC). They have a wonderful location that will put you within walking distance of a ton of good restaurants (at the resorts and Epcot's World Showcase). I think the YC has a very adult atmosphere, and it's very relaxing. I stayed on their concierge level (room 5151) this past December and found it to be a very "pampering" experience. If budget permits, I would definitely try concierge level or even a suite. The BoardWalk Inn has "garden suites" with their own private little garden area with a white picket fence, jacuzzi tub, and loft. They look super nice (we will be staying in one for part of our honeymoon) and tucked away for some calmness and privacy. They are pretty pricey though (regular season they are $600 per night plux tax), but look very nice.
That having been said, another romantic resort area would be the MK monorail resorts. The views of the castle from the Poly's castle view rooms are really neat. I do find that the Poly generally has lots of kids/families at it, but they have never interfered with my relaxation/enjoyment while staying there.